1. Field of the Invention
An embodiment of the present invention relates to a display device. An embodiment of the present invention relates to an electronic device.
2. Description of the Related Art
In recent years, technological development of display devices with higher definition has been advanced.
An example of the display device is an electroluminescent display device (also referred to as an EL display device), or the like (e.g., Patent Document 1). The EL display device has an electroluminescent element (also referred to as an EL element) and a driving transistor for controlling the amount of current supplied to the EL element.
In order that the EL display device may have higher definition, the number of pixels may be increased for higher resolution. In this case, the EL display device needs a reduction in luminance variation among pixels and higher operation speed of a driver circuit. Accordingly, field-effect transistors in the EL display device preferably have high field-effect mobility and small variations in electrical characteristics; for example, a field-effect transistor where a single crystal silicon layer is used for a channel formation region is preferably used.
On the other hand, when the number of pixels is increased while the size of a panel is fixed, the area per pixel is decreased. In addition, pixel area determines the amount of current needed for an EL element. Since the area of an EL element is decreased as a pixel area is decreased, the amount of current supplied to the EL element is required to be reduced. In order to decrease the amount of current supplied to an EL element, current flowing between a source and a drain of a driving transistor (also referred to as drain current) may be reduced, for example.